I. Field of the Invention
The present invention relates generally to a process for producing building materials from recycled paint sludge. More specifically, the present invention relates to a chemical drying process for mixing paint sludge with quick-lime or calcium oxide (CaO) and producing calcium hydroxide Ca(OH).sub.2, a valuable and integral component for use in mortar, concrete, and asphalt. My invention includes a process involving the chemical drying of paint sludge through the use of lime, thus creating a powder made of paint solids and slaked lime suitable as a component in asphalt, concrete and mortar.
Recently, increasing environmental concerns and federal regulations have sought to limit the type and quantity of waste generated by the automotive paint industry. In response to this problem, manufacturers have developed various methods for creating useful byproducts from automotive paint sludge.
When an automobile is painted in a paint booth, the excess paint solids are collected beneath the paint booth, typically in a water-based system. The material recovered from such processes, either by chemical separation, membrane technology, filtration, or scrubbing, is known as paint sludge. Disposal of paint sludge is a problem of considerable complexity that faces paint booth operators. Currently available disposal technology is based upon the principles of incineration, chemical and physical treatment, and solidification. The resulting end product of such technology is a typically used as landfill. However, these paint sludge and products currently include components of concern because of the potential environmental hazards they create. Thus, the use of paint sludge and products in landfilling has its limitations. Accordingly, there is a need for a simple process that effectively uses all of the paint solids generated by a paint booth facility.
Our invention utilizes a chemical treatment process of paint sludge that results in the production of a fine powdered Ca(OH).sub.2 (slaked lime) and dried paint solids. This mixture is an acceptable alternative to a conventional slaked lime used as an admixture for concrete or mortar. The present invention utilizes paint sludge comprising 30-100% by weight paint solids that is mixed with quick-lime. The preferred embodiment of this invention pretreats the sludge with caustic soda (NaOH) in order to react with and reduce any free aluminum to aluminum oxide in the paint sludge. This pretreatment avoids or eliminates bulging which could otherwise cause cracking and crumbling which could weaken or destroy the end cement product. Thus, the present invention provides a superior constituent ingredient for use in the creation of construction materials while providing an efficient method for the recycling of paint sludge.
II. Description of the Prior Art
U.S. Pat. No. 5,160,628 (Gerace et al.) teaches a method for making a filler from automotive paint sludge. Gerace teaches a two step process for handling paint sludge. First, Gerace requires the mechanical removable of water from paint sludge. Second, Gerace uses chemical drying agents to remove further water and to produce a dried paint sludge powder containing uncured polymer.
The present invention avoids the absolute necessity for mechanical water removal that Gerace teaches. Also, Gerace stresses the importance of keeping the temperature of the sludge below 100.degree. F. to avoid curing the polymer resin in the paint sludge. The present invention, by contrast, specifically requires the exothermic reaction that results from mixing quick-lime and water, raising the temperature of the resulting mixture toward the boiling point of water. Further, the exothermic reaction of the present invention results in a greater speed of reaction, thus drying the paint sludge mixture more quickly. Also, the present invention does not necessarily have as strict a limitation with respect to producing cured or uncured polymer resin in the resulting product. Thus, Gerace is directed to a different kind of paint sludge product that is produced through fundamentally different reaction techniques.
U.S. Pat. No. 5,259,977 (Girovich et al.) teaches a method and apparatus for the treatment of sewage sludge. Girovich teaches the desirability of an agglomerization or pelletization step in the treatment of organic sludge. Girovich further discloses the use of quick-lime in the treatment of organic sludge for the purposes of diminishing odors and neutralizing pathogens. The present invention, by contrast, seeks the production of a fine powder admixture for the manufacture of cement. Further, while the present invention uses calcium oxide in the treatment of paint sludge, its use is directed toward the chemical drying of the sludge and creation of a useful resulting product, not the neutralization of organic pathogens.
U.S. Pat. No. 5,004,550 (Beckman et al.) teaches a method of paint sludge conversion for disposal. Beckman teaches the addition of detackification agents to paint sludge in order to float the resulting product out of a paint sludge pit for disposal. Beckman, however, provides no teaching as to any process for reusing paint sludge. Thus, Beckman presents the very problem that the present invention seeks to overcome.
U.S. Pat. No. 5,238,583 (Forston, et al.) teaches a method for converting a contaminated waste material into an innocuous granular substance. Forston specifically teaches the use of a calcium oxide, mixed with an inorganic oxide to reduce a waste sludge to an innocuous granular substance while neutralizing environmentally unacceptable compounds. The present invention, by contrast, is capable of practice with only one chemical drying agent, calcium oxide. Further, the present invention, unlike Forston, seeks to provide an environmentally acceptable reuse for significant volume of paint sludge, rather then merely making such sludge acceptable for landfill placement.
In short, none of the prior art, alone or in combination suggests a process for creating an inexpensive, environmentally desirable admixture for cement with equal or greater functional capability than cement made from ordinary calcium hydroxide. Specifically, none of the prior art discloses adding quick-lime to paint sludge that has been pretreated with caustic soda.